The field of the invention is methods and apparatus for cleaning semiconductor substrates.
During the processing of semiconductor substrates into completed electronic devices such as integrated circuits, microprocessors, or memory chips, it is necessary to clean the semiconductor substrates to remove organic material particle or film contaminants on the surface of the semiconductor substrate. Contaminants that are not removed during the cleaning step reduce the overall yield of the manufacturing process thus reducing the number of useable electronic devices, that can be obtained from a given semiconductor substrate. Contamination is increasingly important in current semiconductor processes, where an increasing number of ever smaller components are placed on a given area of the semiconductor substrate.
The removal of organic materials from semiconductor substrates has generally been accomplished through an oxidation process, in which organic contaminants are either converted completely to CO2 and water, or through partial oxidation, which will disrupt the polymer matrix and facilitate the bulk removal of the contaminating film or layer. One technique for removing organic contaminants uses ozone and deionized (DI) water. This technique can be illustrated in the following chemical reaction:
xe2x80x94CH2xe2x80x94(n)+(3n)O3xe2x86x92(n)CO2+(n)H2Oxe2x80x83xe2x80x83(1)
The use of ozone in DI water, as represented by the above-reaction, has been successfully applied to remove many types of organic contamination, including photoresist films. Other methods of removing organic contaminants from semiconductor substrates have included use of sulfuric acid with hydrogen peroxide and/or ozone. However, use of the ozone and DI water reaction provides cost and environmental benefits over the acid-based removal method. Recent advances in ozone and DI water photoresist stripping have improved the strip rate and performance characteristics of the removal method, making the ozone/DI water method highly competitive with acid-based removal methods.
One of the major limitations of any oxidative cleaning process, including the ozone/DI water method, is that it has limited application on metal films or layers, as many metals will be oxidized along with the organic contaminants. Some metals such as aluminum, when oxidized, form a xe2x80x9chardxe2x80x9d oxide. A hard oxide is an inert, continuous oxide film, which prevents further reaction of the metallic film beyond the surface layer. Other metals such as copper, form a non-passivating oxide, such as CuO. CuO is a black material that is loosely bonded to the reactive copper surface. Thus, as CuO forms on the surface of a semiconductor substrate, it spalls off the surface of the substrate, thereby exposing a fresh layer of Cu that is available for further oxidation.
Consequently, methods for cleaning semiconductor substrates having metal layers often require use of organic-based solvents that dissolve the organic contaminants, rather than oxidizing them. However, organic-based solvents are very expensive and increase the cost of the cleaning process. In addition, organic-based solvents generally create health and environmental concerns.
Difficulties in removing organic contaminants are of special concern with semiconductor substrates that have a surface film or layer of copper (Cu). Electroplated Cu is now being used to provide the interconnect layers on semiconductor wafers. Due to the smaller sizes of the electronic devices formed on the semiconductor substrates, it is becoming increasingly important to remove even smaller contaminants, including organic contaminants, from the semiconductor substrate surface. However, ozone/DI water cleaning is not suitable for semiconductor substrates containing a Cu film or other metal layer subject to oxidation during cleaning.
Thus, there is a need for an improved semiconductor substrate cleaning method. There is also a need for method that suppresses or eliminates the oxidation of conductive films on semiconductor substrates.
In a first aspect of the invention, a method is provided for cleaning organic material from a semiconductor substrate, wherein the semiconductor substrate includes an electrically conductive layer or surface. The semiconductor substrate is immersed in water. The conductive layer is supplied with electrons. Ozone gas is introduced into to the water. This passivates the conductive layer and promotes cleaning. Typically, the conductive layer or surface is a metal, such as copper. The conductive surface may be continuous, such as a plated but not etched substrate, or it may be discontinuous, in the form of pads, runs, vias, etc.
In a second aspect of the invention, the method includes the steps of spraying the semiconductor substrate with water, connecting the conductive layer or surface to a source of electrons, and providing ozone gas to the conductive layer.
In another aspect of the invention, an apparatus for suppressing the oxidation of a conductive layer or surface on a semiconductor substrate, includes a fixture for holding the substrate, a bath of fluid (typically water), ozone gas within the fluid bath, and a source of electrons electrically connected to the conductive layer.
In still another aspect of the invention, an apparatus for suppressing the oxidation of a conductive surface on a semiconductor substrate, includes a fixture for holding the substrate, a sprayer for spraying a fluid, such as water, onto the conductive surface, an ozone gas source, and a source of electrons electrically connected to the conductive surface or section of the semiconductor substrate.
In still another aspect of the invention, a method of cleaning organic material from a semiconductor substrate includes the steps of immersing the semiconductor substrate in water, contacting the conductive film to a cathode of a DC electrical power source (such as a DC power supply or a battery), preferably placing an anode of the DC electrical source adjacent to the surface of the semiconductor substrate, and providing ozone gas into the water.
In yet another aspect of the invention a method of cleaning organic material from a semiconductor substrate having any conductive metal surface areas, includes the steps of spraying the metal surfaces with water, connecting the metal surface areas to a cathode of a DC electrical source, optionally placing an anode of the DC electrical source adjacent to the surface of the metal areas, and providing ozone gas around the metal areas.
In another aspect of the invention, an apparatus for suppressing the oxidation of a conductive film on a semiconductor substrate includes a fixture for holding the semiconductor substrate, a water bath, a supply of ozone gas, and a cathode of a DC electrical power source electrically connected to the conductive film. The anode of the DC electrical power source is positioned adjacent to the surface of the semiconductor substrate including the conductive film thereon.
In another aspect of the invention, a device for suppressing the oxidation of a conductive film contained on a semiconductor substrate includes a fixture, for holding the semiconductor substrate, a sprayer for spraying water onto the semiconductor substrate, a supply of ozone gas, a cathode of a DC electrical power source electrically connected to the conductive film of the semiconductor substrate. The anode of the DC electrical source is positioned adjacent to the surface of the semiconductor substrate including the conductive film thereon.
Accordingly, it is an object of the invention to provide improved methods and devices for cleaning a semiconductor substrate. It is a further object of the invention to provide methods and apparatus for suppressing oxidation of conductive films on semiconductor substrates. Other objects and advantages will appear below.
The invention resides not only in the combinations described above, but also in subcombinations of them.